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Reoccurring EML Issue

Discussion in 'Gen 4 Prius Main Forum' started by AdeelUK, Oct 19, 2020.

  1. AdeelUK

    AdeelUK Junior Member

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    I have a Toyota Prius 2016 4th Generation (new shape).

    I noticed the Engine Management Light kept coming on intermittently. Sometimes once a month, once a week or even after every couple of days.

    I had it diagnosed it on a normal diagnostic machine from a local garage & the Fault code kept coming back as ignition coil plugs 1,2,3 & 4 (A,B,C & D).

    I changed all 4 Ignition Coil plugs & All 4 Spark Plugs all brand new from Toyota original parts.

    The EML came back on.

    I then took it to straight to Toyota & their diagnostic machine also showed the same faults with the ignition coil plugs but as they had already been changed they recommended I change the cars Auxiliary battery & replace the hybrid battery filters as they were quite dirty - I got the work carried out by them.

    The EML was STILL ON when I went to pick the car up from them.

    Toyota are now saying that they have exhausted all avenues & they can only suggest it’s 1 of 2 things - either the ECU has an issue/needs replacing or the wiring loom leading from the ignition coils to the ECU maybe faulty.

    I got a local garage to check the wiring loom to see if there were any signs of any loose connections, cuts or any tampering but there is no sign of this at all, all the wiring looks genuine & clean & untouched/untampered with.

    I find it hard to believe that there is an issue with the ECU & there is no way of testing the old ECU, there is no Auto Electrician in the country that will touch it as it is a hybrid & they simply don’t have the software to test them. Toyota have also said they cannot test the old ECU & even if I replace the old ECU with a new one they will still not guarantee that this will solve the EML issue.

    Please can anyone help me??

    Do you have any suggestions ? Have you heard of or come across anything like this before with my particular car? It is really important I get to the root of this problem as I have already spent so much time & money on the car & it has still not sorted this issue out & my vehicle is used as a taxi so it is important for work purposes also.

    Look forward to hearing from you.

    Many Thanks in advance.
     
    #1 AdeelUK, Oct 19, 2020
  2. pianewman

    pianewman Active Member

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    Just curious, how many miles?
     
    #2 pianewman, Oct 20, 2020
  3. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Any evidence of mice/rats chewing on the wiring?
     
    #3 Mendel Leisk, Oct 20, 2020
  4. CooCooCaChoo

    CooCooCaChoo Senior Member

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    Have you had the technical service bulletin involving the wiring harness rubbing and shorting in the engine bay done?

    2017 TOYOTA PRIUS | NHTSA
     
    #4 CooCooCaChoo, Oct 20, 2020
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  5. AdeelUK

    AdeelUK Junior Member

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    Hi pianewman

    it’s just hit 103k - hence also past the Toyota warranty cover.
     
    #5 AdeelUK, Oct 21, 2020
  6. AdeelUK

    AdeelUK Junior Member

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    hi mendel leisk

    this was one of the first things I checked
    As the Ignition coils & ECU communicate with each other directly i got a very thorough mechanic to check the wiring loom & there were no signs whatsoever of the wiring been chewed, damaged or tampered with - it all looks original & untouched. Even Toyota agreed that the wiring didn’t look out of place.
     
    #6 AdeelUK, Oct 21, 2020
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  7. AdeelUK

    AdeelUK Junior Member

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    Hi coocoocachoo

    I’ve already been on the Toyota website & checked. Also When it went in with Toyota they checked for any recalls - the only one was a seat belt recall which they sorted out On the day - nothing else is outstanding.
     

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    #7 AdeelUK, Oct 21, 2020
  8. robsnyder20

    robsnyder20 Active Member

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    I was thinking the same thing. Perhaps it was just taped when it should have been replaced. Hopefully you get to the root cause of this. 103K is WAY too early for this type of issue. Frustrating for sure!
     
    #8 robsnyder20, Oct 21, 2020
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  9. Elektroingenieur

    Elektroingenieur Senior Member

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    Do you know the actual diagnostic trouble codes (DTCs) that were found?

    For example, P035113 (P0351) is Ignition Coil “A” Circuit Open, and P035213, P035313, and P035413 are the same for “B,” “C,” and “D.” For every DTC, the Repair Manual (more info) gives a step-by-step troubleshooting procedure, developed to help find and fix problems at the least cost for parts and labor.

    Are there any drivability symptoms or unusual noises?
    Those are likely trouble areas, but there could be other possibilities. For example, has anyone made sure that the bolt at ground point CB, on the right side of the engine, is torqued to specification (10.0 N·m)?
    Did they do a visual inspection only, or did they also do the voltage and resistance checks in the Repair Manual procedure for P035113/P035213/P035313/P035413? I’ve seen more than one wire harness (loom) that looked beautiful but had a open splice, ground fault, or other electrical problem.

    Also, has anyone used an oscilloscope to check the IGT1/IGT2/IGT3/IGT4 and IGF1 signals?
    In Toyota’s servicing strategy, most faults in the engine control module (ECM) itself are identified by exclusion: if you’ve checked for all of the other likely causes, then you replace the ECM as a last resort.

    The dealer is correct that they can’t test the ECM itself—they have neither the equipment nor the technical information needed for this—but I wonder how thoroughly they’ve done the other checks specified in the Repair Manual for whatever DTCs have been stored.
    The problem addressed by the 18SMD-076 (Europe) or J0T (U.S.) safety recall is unlikely to be related, I think: the affected part of the engine wire harness was the branch to connector C33 on the inverter with converter assembly (power control unit), which isn’t part of the ignition circuits. If the engine wire harness was already damaged and had to be replaced as part of the recall repair, however, the replacement harness might be faulty or have been improperly installed.
     
    #9 Elektroingenieur, Oct 22, 2020
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  10. CooCooCaChoo

    CooCooCaChoo Senior Member

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    ^^^ This guy's got all the good questions and comments. Only other thing I can add in is WHEN does the light come on? Intermittent problems are the hardest to diagnose because of their very nature.

    Does it come on in the morning when the car is cold?
    Does it come on when the car is hot?
    Does it come on after the car has been in electric mode?
     
    #10 CooCooCaChoo, Oct 23, 2020
  11. AdeelUK

    AdeelUK Junior Member

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    Hey Guys,

    sorry for the late reply but I finally got to the root cause of all my EML issues..(showing ignition coil ABCD/1234 on diagnostic)

    to cut a long story short my Prius went back to the Toyota Dealership for the 4th time, this time on the back of a AA recovery Truck as the EML issue had gotten so bad the car just wouldn’t move when in gear (start only).

    Seems like Toyota now took me a lot serious than on previous visits & had no choice but to delve deeper into finding the issue & finally found the problem...
    It was one poxy little blue wire in the wiring loom coming from the ECU side (going to the ignition coils) - it was literally hanging on by a thread & when they got to the wire it came apart (as per the image I’ve uploaded).
    They managed to repair the old wire (obviously at a Toyota Premium cost) but I’m just so glad my nightmare is over, having already spent so much money on it second guessing the issue & changing parts I didn’t have to. Ah well you live & you learn.

    Many thanks for all your help & guidance throughout
     

    Attached Files:

    #11 AdeelUK, Nov 14, 2020
    robsnyder20, Henrik Helmers, -Yousef- and 1 other person like this.
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